1. Field of the Invention
This invention generally relates to bicycles. More specifically, the present invention relates to an apparatus for a crank detachable holder used in a rotation detecting apparatus that detects rotation of a bicycle crank.
2. Background Information
Recently, bicycles have been equipped with a cycling computer, which provides information such as speed, cadence, rider inputs, etc. Cycling computers can make bicycle riding more enjoyable to the rider (e.g. by displaying various information to the rider such as time, elapsed time, speed, distance, average speed, etc.). Conventionally, a rotation detecting apparatus is attached to the bicycle to a wheel or a crank arm for detecting the rotation of the wheel or the crank arm so that a cycle computer may use the detected rotations to calculate and display the bicycle speed or pedal cadence to the rider. A conventional rotation detecting apparatus typically comprises a magnet mounted to a rotating part and a magnetic sensor mounted to a fixed part such as the bicycle frame. The magnetic sensor may comprise a reed switch, a Hall-effect element, etc., and it usually is mounted in a position that faces the magnet at some time during rotation of the bicycle part. For example, when used to calculate bicycle speed, the magnet may be mounted to the spoke of a wheel, and the magnetic sensor may be mounted to the front fork. When used to calculate pedal cadence, the magnet may be mounted to the crank arm, and the magnetic sensor may be mounted to either the seat tube or the down tube of the bicycle frame.
One example of a conventional rotation detecting apparatus is disclosed in U.S. Pat. No. 7,061,228 B2. In this patent, a special fixing structure is used to attach a magnet to the crank arm of cadence sensor. Instead of using the special fixing structure, magnets were more simply attached to the crank arm by a rubber band or a band fastener.